Seat suspension mechanisms support a person sitting on the seat while providing maximum comfort. These mechanisms are designed to provide comfort to the occupant while minimizing and absorbing or dampening bumps and jolts due to uneven, rough or rugged terrain the vehicle encounters. Design criteria include seat vibration and frequency of the seat and suspension of the seat and the vehicle, space limitation under the seat and above the seat to overhead restraints, the type of terrain likely to be encountered, limits of seat travel up and down to absorb shocks during operation, components costs, durability, and the like. The design criteria are particularly critical and generally more complicated for off-road vehicles, such as tractors, lift-trucks, heavy equipment, earth moving vehicles, and the like. These off-road vehicles have either relatively heavy-duty or no shock absorbing suspensions between the wheels and the chassis that do not prevent jolts, bumps, vibrations, and shocks from reaching the driver. Thus for these vehicles the seat and seat suspension must safely dampen and absorb these transmitted jolts in a safe manner while providing comfort and reducing fatigue. Such prior art suspensions have not adequately provided horizontal stability to enable the driver to maintain control when encountering rough terrain. As an example, it is not safe for the driver to be thrown fore-and-aft as the seat moves up and down due to rough terrain.
Typical prior art suspension mechanisms are illustrated and described in U.S. Pat. No. 4,241,894 to Okuyama, FIGS. 3a, 3b, and /3c. Other prior art suspension mechanisms, as illustrated in FIG. 1c of Okuyama employ a parallelogram arrangement of bi-arm linkage with one pair of adjacent ends of the arms pivotally connected to a bracket extending downwardly from the cushion frame and the opposite ends of the arms pivotally connected to the deck frame of the vehicle, with all pivot connections in a single plane. Biasing springs connected to the cushion frame or to arms and to the deck provide a cushioning effect. These prior art figures and description from Okuyama are incorporated herein by reference thereto. Still other prior art suspension mechanisms employ a scissors arrangement of bi-arm linkage with one pair of adjacent ends of the arms pivotally connected to the cushion frame and the opposite ends of the arms pivotally connected to the deck frame of the vehicle. Again biasing springs provide a cushioning effect by dampening the jolting movement of vehicle caused by roadway undulations and bumps. An attempt is made to choose the spring characteristics to bias rather than match the amplitude and frequency of the road bumps, in an effort to smooth the ride to avoid a bouncing effect.
Another typical prior art seat suspension apparatus in used on KUBOTA® vehicles includes four bellcranks connecting springs to bias movement of the seat frame. As illustrated in the schematic drawing of a side view of one of the bellcranks 11 of the KUBOTA® apparatus shown in FIG. 8, pivot point 12 is connected to and located down at the base, the angle 15 between lines from pivot point 12 to connecting point 13 to the seat frame and from point 12 to connecting point 14 to the spring bias opens upwardly, and the spring biasing connecting point 14 is on an upper directed arm form the pivot point. As the seat is lowered and raised bellcrank 11 rotates through angle β with up and down movement c of the seat frame due to the weight of the person sitting on the seat and jolts from a rough roadway, angle 15 moves counter-clockwise as the seat is compressed and unfavorably the seat also moves fore-and-aft distance b, which is common. The bellcranks of the Kubota apparatus pivot from a non-upraised pivot point on the base frame with the two arms of each of the bellcranks extending upwardly at an acute angle from each other. A spring bias pulls horizontally from a distal end of one of the ends against force applied to the distal end of the second upright arm in an opposite direction as the seat frame is depressed. No portion of this bellcrank moves into spaces between the slide rails below the lower frame or into the set cushion area and so has only about one-half as much vertical travel for similar profile height. All of these elements of these prior art bellcranks are essentially opposite or contrary to the present invention, resulting in, among other deficiencies, the substantial fore and aft movement during compression and decompression of the suspension mechanism as well as higher spring bias per distance of movement close to upper position and lower bias per distance of movement as the seat moves toward the lowest position, resulting in a harsher ride. Other limitations of these seat suspension mechanisms and the ones that follow include complexity, high weight, higher costs, and relatively high profile inasmuch as the height of the seat above the vehicle frame is almost always at a premium, either to provide space under the seat or due to restricted head room for safety of the operator. One of the reasons the prior art suspension mechanisms have a high profile is that they have separate upper and lower frames/brackets.
U.S. Pat. No. 5,014,960 to Kimura discloses a seat suspension mechanism directed to absorbing horizontal fore-and-aft impact or jolting applied to the seat. U.S. Pat. No. 4,520,986 to Liljequist et al disclosed a seat assembly with reduced elevational space requirements. U.S. Pat. No. 5,014,960 to Harney discloses a seat adjustor mechanism with bellcrank with angles between diverging lines from the pivot point to the two connecting points of the bellcranks greater than 90 degrees and a pivot point that is not raised above the seat frame. U.S. Pat. No. 5,222,709 to Culley, Jr. et al discloses a scissor-type suspension mechanism with a bellcrank used for adjustment. U.S. Pat. No. 6,264,158 to Downey et al discloses a support structure for a vehicle seat assembly with fore-aft adjustment. U.S. Pat. No. 6,520,474 to Toshida et al discloses a slice mechanism for a vehicle seat. U.S. Patent Application Publication 2003/0201660 to Janscha et al discloses a seat suspension mechanism with a bellcrank with angles between diverging lines from the pivot point to the two connecting points of the bellcranks greater than 90 degrees and a pivot point that is not raised to extend above the seat frame. U.S. Pat. No. 5,938,164 to Kargol et al discloses a seat adjuster for vehicle seat assemblies. U.S. Pat. No. 6,695,275 to Schuler et al discloses a device for longitudinal adjustment for vehicle seats. U.S. Patent Application Publication 2005/0006937 to Takata et al discloses a lifter for adjusting the height of a vehicle seat frame with a magnetic damper. U.S. Patent Application Publication 2005/0001133 to Bostrom et al discloses a scissor-type seat suspension mechanism for motor vehicles. U.S. Pat. No. 5,794,911 to Hill discloses a suspension seat using a parallelogram suspension mechanism. U.S. Patent Application Publication 2004/0144906 to Hill et al discloses a vehicle suspension mechanism with a bellcrank that operates differently and does not include the elements of the bellcranks of the present invention. U.S. Pat. No. 6,755,469 to Akaike et al discloses a typical parallelogram suspension mechanism. U.S. Pat. No. 6,851,753 to Akaike et al discloses a suspension system similar to his prior patent except for pivot members from the seat frame to a slide connection in the base frame. U.S. Pat. No. 6,830,297 to Gordon discloses a suspension seat with a link between the spring and the suspension mechanism similar to the prior art described above. U.S. Pat. No. 6,773,049 to Rupiper et al. discloses a suspension seat using a parallelogram suspension mechanism. U.S. Pat. No. 6,776,384 to Igarashi discloses a seat suspension using a typical scissor cross-member suspension mechanism.
None of these devices disclose or even suggest the use of the bellcranks and suspension apparatus of the present invention, nor do they satisfy the needs of the prior art described herein above or attain the objects of the present invention provided herein below.